Over the course of their lives the average American will undergo nearly nine surgical procedures, many related to diseases of the digestive track or conditions associated with obesity. Despite being some of the most commonly performed interventions, most of these procedures have not been subjected to rigorous scientific evaluation. For almost all of these procedures, fundamental questions regarding surgical epidemiology, clinical effectiveness, best practices to accomplish best outcomes, population-level results, patient-reported perspectives, and cost considerations have yet to be addressed. As healthcare delivery is reformed and as we strive towards building a learning healthcare system, addressing these questions is critical. One reason for the shortfall in rigorous clinical research in surgery is a paucity of formal, health services and comparative effectiveness research training for surgeons. To address this need, we propose the continuation and expansion of the University of Washington's National Research Service Award (NRSA) fellowship in clinical, health services, comparative effectiveness and patient-centered outcomes research for surgeons. This fellowship involves didactic training and practical experience in advanced research methodology focused on interventions related to the gastrointestinal system, obesity, and obesity-associated conditions. The training is focused in 6 areas (research using observational data, patient-centered outcome and preference assessment, health economics and behavioral economics in healthcare, policy and implementation science research, clinical / translational research, and research operations management) and is intended to develop surgeon- scholars who will be successful scientists and help build and advance the goals of a learning healthcare system. The didactic component of this fellowship includes coursework that results in a Masters of Public Health (MPH) or Masters in Science (MS) degree through the University of Washington School of Public Health and Community Medicine, with additional coursework and certificate training in the PhD candidate-training program of the Departments of Health Services and Pharmacy. All trainees complete a set of projects and studies representing a wide spectrum of research methods and approaches. The trainee's experience is fostered by a structured mentorship program with seasoned investigators who have a career commitment to training and career success in high-level research and integrating evidence into practice change. The T32 Fellows also participate in unique community, regional and national learning healthcare system programs including Washington State's Comparative Effectiveness Research Translation Network (CERTAIN),3 the Surgical Care and Outcomes Assessment Program (SCOAP)4 and a program aimed at optimizing patients before hospitalization called Strong for Surgery (strongforsurgery.org). Trainees participate in the NRSA fellowship for two years and then serve an additional 5-7 years of additional postdoctoral clinical training as general or specialty surgeons in the fields of advanced laparoscopy, foregut, hepatobiliary, colorectal, or bariatric surgery before obtaining academic faculty positions. The current NRSA fellowship program supports one new trainee per year, and because of program success, mentor capacity and trainee demand we are requesting an expansion to two new trainees per year.